[libcxx][SystemZ][z/OS] added internal_threading_support.h

[DanielMcIntosh-IBM]

Summary

This is a different approach to adding support for z/OS POSIX(OFF) based on the suggestions in D110349.
However, since z/OS still needs to use the pthread version of the __threading_support API, instead of _LIBCPP_HAS_THREAD_API_EXTERNAL we implement something very close to _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL.

We couldn't quite use _LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL for two reasons: First, we only want to affect libcxx's internal uses of __threading_support (i.e. those inside libcxx/src not libcxx/include). Second, we don't want to affect anything in the C++11 Threading Support Library, since the user shouldn't be using that anyways if the base threading support library (e.g. pthread) isn't available.

This is the 4th of 4 changes to add support for POSIX(OFF) on z/OS.
See D117366 for more background, and D110349 for discussion of an alternative implementation.

Depends on D117370, D117372, D117373

[DanielMcIntosh-IBM]

Update Documentation

[DanielMcIntosh-IBM]

Remove documentation update (and move to D117372, since it's more appropriate there)

[DanielMcIntosh-IBM]

libcxx/src/include/internal_threading_support.h

265–276

To me, this is horrendous, and a very strong reason to prefer what I proposed in D113054. Even if we go with the approach outlined in this PR for everything else except exception storage, I think that at the very least the runtime-dependent threading changes should be allowed to creep out of internal_threading_support.h and into cxa_exception_storage.cpp.

We may also not have any choice in the matter when adding support for a platform like AIX where __libcpp_is_threading_api_enabled() can change during program execution.

[zibi]

Please see the new version in D120348.

libcxx/include/__threading_support

else
     __ts.tv_nsec = 999999999; // (10^9 - 1)
   }
 
   return __ts;
 }
 
 } // namespace __thread_detail
 
-#if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
+#if defined(_LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL)
+// Empty - function definitions are provided by src/include/internal_threading_support.h
+#if !defined(_LIBCPP_BUILDING_LIBRARY)
+#error _LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL is only intended to protect internal \
+       uses of __threading_support by libcxx.
+#endif
+
+#elif defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
 
 _LIBCPP_HIDE_FROM_ABI inline
 int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t *__m)
 {
   pthread_mutexattr_t attr;
   int __ec = pthread_mutexattr_init(&attr);
   if (__ec)
     return __ec;

libcxx/src/CMakeLists.txt

set(LIBCXX_SOURCES
   condition_variable_destructor.cpp
   exception.cpp
   functional.cpp
   future.cpp
   hash.cpp
   include/apple_availability.h
   include/atomic_support.h
   include/config_elast.h
+  include/internal_threading_support.h
   include/refstring.h
   include/ryu/common.h
   include/ryu/d2fixed.h
   include/ryu/d2fixed_full_table.h
   include/ryu/d2s.h
   include/ryu/d2s_full_table.h
   include/ryu/d2s_intrinsics.h
   include/ryu/digit_table.h

libcxx/src/debug.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "__config"
 #include "__debug"
 #include "functional"
 #include "algorithm"
 #include "string"
 #include "cstdio"
 #include "__hash_table"
 #ifndef _LIBCPP_HAS_NO_THREADS
-#include "__threading_support"
+#include "include/internal_threading_support.h"
 #if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
 #pragma comment(lib, "pthread")
 #endif
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 std::string __libcpp_debug_info::what() const {

libcxx/src/include/internal_threading_support.h

+//===----------------------------------------------------------------------===////
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===////
+
+#ifndef _LIBCPP_INTERNAL_THREADING_SUPPORT_H
+#define _LIBCPP_INTERNAL_THREADING_SUPPORT_H
+
+/** internal_threading_support.h - Equivalent to __threading_support, but for internal uses that are
+ * not related to the C++11 Threading Library. These should all be within code that is compiled into
+ * the libcxx library rather than potentially #included by user code.
+ *
+ * See libcxx/docs/DesignDocs/InternalThreadSynchronization.rst for details.
+ *
+ * Any use of the C++11 Thread Support Library (e.g. std::mutex) without an underlying thread
+ * library available is user error, so we want files like mutex.cpp to use the definitions from
+ * __threading_support. For that reason, _LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL needs to be defined
+ * here instead of in __config.
+ *
+ * Any platforms which cannot determine during compilation of libc++ the availability of a thread
+ * library such as pthreads should define `_LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL` before
+ * <__threading_support> is #included, and provide definitions for
+ * `__libcpp_is_threading_api_enabled()` and `__libcpp_might_have_multiple_threads()`
+ */
+
+#if !defined(_LIBCPP_BUILDING_LIBRARY)
+#  error internal_threading_support.h is only intended for internal use by libcxx
+#endif
+
+#ifdef _LIBCPP_THREADING_SUPPORT
+#  error internal_threading_support.h must be included before <__threading_support>
+#endif
+
+#if defined(__MVS__)
+// Tell __threading_support not to provide function definitions, since we provide them here
+#  define _LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL
+#endif
+
+#include <__threading_support>
+
+#if defined(_LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL) && !defined(_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
+
+_LIBCPP_THREAD_ABI_VISIBILITY
+bool __libcpp_is_threading_api_enabled();
+
+_LIBCPP_THREAD_ABI_VISIBILITY
+bool __libcpp_might_have_multiple_threads();
+
+#  if defined(__MVS__)
+#    include "ceeedb.h"
+/// On z/OS some posix functions can be enabled/disabled at runtime.
+/// However, the enabled/disabled status should not change over the life of the process.
+bool __libcpp_is_threading_api_enabled() {
+  static bool __posix_on = __libcpp_ceeedb_posix();
+  return __posix_on;
+}
+bool __libcpp_might_have_multiple_threads() { return __libcpp_ceeedb_multithread(); }
+#  endif
+
+//===----------------------------------------------------------------------===//
+//    Definitions which would normally be provided by __threading_support
+//===----------------------------------------------------------------------===//
+
+#  if defined(_LIBCPP_HAS_THREAD_API_PTHREAD)
+
+int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+
+  pthread_mutexattr_t attr;
+  int __ec = pthread_mutexattr_init(&attr);
+  if (__ec)
+    return __ec;
+  __ec = pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+  if (__ec) {
+    pthread_mutexattr_destroy(&attr);
+    return __ec;
+  }
+  __ec = pthread_mutex_init(__m, &attr);
+  if (__ec) {
+    pthread_mutexattr_destroy(&attr);
+    return __ec;
+  }
+  __ec = pthread_mutexattr_destroy(&attr);
+  if (__ec) {
+    pthread_mutex_destroy(__m);
+    return __ec;
+  }
+  return 0;
+}
+
+int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_mutex_lock(__m);
+}
+
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return true;
+  return pthread_mutex_trylock(__m) == 0;
+}
+
+int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_mutex_unlock(__m);
+}
+
+int __libcpp_recursive_mutex_destroy(__libcpp_recursive_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  return pthread_mutex_destroy(__m);
+}
+
+int __libcpp_mutex_lock(__libcpp_mutex_t* __m) {
+  // All libcxx-internal locks are released before we run any code which could
+  // spawn a thread, so we can safely skip mutex acquisition when there's only
+  // one thread (even if the threading API is enabled).
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_mutex_lock(__m);
+}
+
+bool __libcpp_mutex_trylock(__libcpp_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return true;
+  return pthread_mutex_trylock(__m) == 0;
+}
+
+int __libcpp_mutex_unlock(__libcpp_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_mutex_unlock(__m);
+}
+
+int __libcpp_mutex_destroy(__libcpp_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  return pthread_mutex_destroy(__m);
+}
+
+// Condition Variable
+int __libcpp_condvar_signal(__libcpp_condvar_t* __cv) {
+  // If we're the only thread, there's no one to signal to, skip it
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_cond_signal(__cv);
+}
+
+int __libcpp_condvar_broadcast(__libcpp_condvar_t* __cv) {
+  // If we're the only thread, there's no one to broadcast to, skip it
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return pthread_cond_broadcast(__cv);
+}
+
+int __libcpp_condvar_wait(__libcpp_condvar_t* __cv, __libcpp_mutex_t* __m) {
+  // If we're the only thread, there's no one to wake us up, so this is a deadlock
+  assert(__libcpp_might_have_multiple_threads());
+  return pthread_cond_wait(__cv, __m);
+}
+
+int __libcpp_condvar_timedwait(__libcpp_condvar_t* __cv, __libcpp_mutex_t* __m, __libcpp_timespec_t* __ts) {
+  if (!__libcpp_is_threading_api_enabled()) {
+    // With nobody to wake us up, this is equivalent to a sleep
+    // TODO: actually wait until __ts, and replace this with
+    // `if(!__libcpp_might_have_multiple_threads())`
+    return ETIMEDOUT;
+  }
+  return pthread_cond_timedwait(__cv, __m, __ts);
+}
+
+int __libcpp_condvar_destroy(__libcpp_condvar_t* __cv) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  return pthread_cond_destroy(__cv);
+}
+
+// Execute once
+int __libcpp_execute_once(__libcpp_exec_once_flag* flag, void (*init_routine)()) {
+  if (!__libcpp_is_threading_api_enabled()) {
+    if (*flag == _LIBCPP_EXEC_ONCE_INITIALIZER) {
+      init_routine();
+      // TODO: In order for this to work when __libcpp_is_threading_api_enabled() can change during
+      // program execution, we have to write the same value pthread_once would.
+      // For glibc this seems to be 2, but it could vary.
+      *flag = 2;
+    }
+    return 0;
+  }
+
+  return pthread_once(flag, init_routine);
+}
+
+// Thread id
+// Returns non-zero if the thread ids are equal, otherwise 0
+bool __libcpp_thread_id_equal(__libcpp_thread_id t1, __libcpp_thread_id t2) { return t1 == t2; }
+
+// Returns non-zero if t1 < t2, otherwise 0
+bool __libcpp_thread_id_less(__libcpp_thread_id t1, __libcpp_thread_id t2) { return t1 < t2; }
+
+// Thread
+bool __libcpp_thread_isnull(const __libcpp_thread_t* __t) { return __libcpp_thread_get_id(__t) == 0; }
+
+int __libcpp_thread_create(__libcpp_thread_t* __t, void* (*__func)(void*), void* __arg) {
+  assert(__libcpp_is_threading_api_enabled());
+  return pthread_create(__t, nullptr, __func, __arg);
+}
+
+__libcpp_thread_id __libcpp_thread_get_current_id() {
+  assert(__libcpp_is_threading_api_enabled());
+  const __libcpp_thread_t thread = pthread_self();
+  return __libcpp_thread_get_id(&thread);
+}
+
+__libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t* __t) {
+#    if defined(__MVS__)
+  return __t->__;
+#    else
+  return *__t;
+#    endif
+}
+
+int __libcpp_thread_join(__libcpp_thread_t* __t) {
+  assert(__libcpp_is_threading_api_enabled());
+  return pthread_join(*__t, nullptr);
+}
+
+int __libcpp_thread_detach(__libcpp_thread_t* __t) {
+  assert(__libcpp_is_threading_api_enabled());
+  return pthread_detach(*__t);
+}
+
+void __libcpp_thread_yield() {
+  if (!__libcpp_might_have_multiple_threads())
+    return;
+  sched_yield();
+}
+
+void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns) {
+  assert(__libcpp_is_threading_api_enabled());
+  __libcpp_timespec_t __ts = __thread_detail::__convert_to_timespec(__ns);
+  while (nanosleep(&__ts, &__ts) == -1 && errno == EINTR)
+    ;
+}
+
+// Thread local storage
+int __libcpp_tls_create(__libcpp_tls_key* __key, void (*__at_exit)(void*)) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  return pthread_key_create(__key, __at_exit);
+}
+
+void* __libcpp_tls_get(__libcpp_tls_key __key) {
+  // ugly and devious way of getting cxa_exception_storage to work, but necessary if we want to
+  // keep all the runtime-dependent threading changes contained within internal_threading_support.h
+  if (!__libcpp_is_threading_api_enabled()) {
+    static struct {
+      void* caughtExceptions;
+      unsigned int uncaughtExceptions;
+    } eh_globals;
+    return &eh_globals;
+  }
+  // TODO: this won't work if __libcpp_is_threading_api_enabled() can change during program
+  // execution, because we may have skipped pthread_key_create()
+  return pthread_getspecific(__key);
+}
+
+int __libcpp_tls_set(__libcpp_tls_key __key, void* __p) {
+  assert(__libcpp_is_threading_api_enabled());
+  return pthread_setspecific(__key, __p);
+}
+
+#  elif defined(_LIBCPP_HAS_THREAD_API_C11)
+
+int __libcpp_recursive_mutex_init(__libcpp_recursive_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+
+  return mtx_init(__m, mtx_plain | mtx_recursive) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_recursive_mutex_lock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return mtx_lock(__m) == thrd_success ? 0 : EINVAL;
+}
+
+bool __libcpp_recursive_mutex_trylock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return true;
+  return mtx_trylock(__m) == thrd_success;
+}
+
+int __libcpp_recursive_mutex_unlock(__libcpp_recursive_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return mtx_unlock(__m) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_recursive_mutex_destroy(__libcpp_recursive_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  mtx_destroy(__m);
+  return 0;
+}
+
+int __libcpp_mutex_lock(__libcpp_mutex_t* __m) {
+  // All libcxx-internal locks are released before we run any code which could
+  // spawn a thread, so we can safely skip mutex acquisition when there's only
+  // one thread (even if the threading API is enabled).
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return mtx_lock(__m) == thrd_success ? 0 : EINVAL;
+}
+
+bool __libcpp_mutex_trylock(__libcpp_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return true;
+  return mtx_trylock(__m) == thrd_success;
+}
+
+int __libcpp_mutex_unlock(__libcpp_mutex_t* __m) {
+  // See __libcpp_mutex_lock for an explaination of why this is safe
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return mtx_unlock(__m) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_mutex_destroy(__libcpp_mutex_t* __m) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  mtx_destroy(__m);
+  return 0;
+}
+
+// Condition Variable
+int __libcpp_condvar_signal(__libcpp_condvar_t* __cv) {
+  // If we're the only thread, there's no one to signal to, skip it
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return cnd_signal(__cv) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_condvar_broadcast(__libcpp_condvar_t* __cv) {
+  // If we're the only thread, there's no one to broadcast to, skip it
+  if (!__libcpp_might_have_multiple_threads())
+    return 0;
+  return cnd_broadcast(__cv) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_condvar_wait(__libcpp_condvar_t* __cv, __libcpp_mutex_t* __m) {
+  // If we're the only thread, there's no one to wake us up, so this is a deadlock
+  assert(__libcpp_might_have_multiple_threads());
+  return cnd_wait(__cv, __m) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_condvar_timedwait(__libcpp_condvar_t* __cv, __libcpp_mutex_t* __m, timespec* __ts) {
+  if (!__libcpp_is_threading_api_enabled()) {
+    // With nobody to wake us up, this is equivalent to a sleep
+    // TODO: actually wait until __ts, and replace this with
+    // `if(!__libcpp_might_have_multiple_threads())`
+    return ETIMEDOUT;
+  }
+  int __ec = cnd_timedwait(__cv, __m, __ts);
+  return __ec == thrd_timedout ? ETIMEDOUT : __ec;
+}
+
+int __libcpp_condvar_destroy(__libcpp_condvar_t* __cv) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  cnd_destroy(__cv);
+  return 0;
+}
+
+// Execute once
+int __libcpp_execute_once(__libcpp_exec_once_flag* flag, void (*init_routine)(void)) {
+  if (!__libcpp_is_threading_api_enabled()) {
+    if (*flag == _LIBCPP_EXEC_ONCE_INITIALIZER) {
+      init_routine();
+      // TODO: In order for this to work when __libcpp_is_threading_api_enabled() can change during
+      // program execution, we have to write the same value ::call_once would.
+      // For glibc this seems to be 2, but it could vary.
+      *flag = 2;
+    }
+    return 0;
+  }
+
+  ::call_once(flag, init_routine);
+  return 0;
+}
+
+// Thread id
+// Returns non-zero if the thread ids are equal, otherwise 0
+bool __libcpp_thread_id_equal(__libcpp_thread_id t1, __libcpp_thread_id t2) { return thrd_equal(t1, t2) != 0; }
+
+// Returns non-zero if t1 < t2, otherwise 0
+bool __libcpp_thread_id_less(__libcpp_thread_id t1, __libcpp_thread_id t2) { return t1 < t2; }
+
+// Thread
+bool __libcpp_thread_isnull(const __libcpp_thread_t* __t) { return __libcpp_thread_get_id(__t) == 0; }
+
+int __libcpp_thread_create(__libcpp_thread_t* __t, void* (*__func)(void*), void* __arg) {
+  assert(__libcpp_is_threading_api_enabled());
+  int __ec = thrd_create(__t, reinterpret_cast<thrd_start_t>(__func), __arg);
+  return __ec == thrd_nomem ? ENOMEM : __ec;
+}
+
+__libcpp_thread_id __libcpp_thread_get_current_id() {
+  assert(__libcpp_is_threading_api_enabled());
+  return thrd_current();
+}
+
+__libcpp_thread_id __libcpp_thread_get_id(const __libcpp_thread_t* __t) { return *__t; }
+
+int __libcpp_thread_join(__libcpp_thread_t* __t) {
+  assert(__libcpp_is_threading_api_enabled());
+  return thrd_join(*__t, nullptr) == thrd_success ? 0 : EINVAL;
+}
+
+int __libcpp_thread_detach(__libcpp_thread_t* __t) {
+  assert(__libcpp_is_threading_api_enabled());
+  return thrd_detach(*__t) == thrd_success ? 0 : EINVAL;
+}
+
+void __libcpp_thread_yield() {
+  if (!__libcpp_might_have_multiple_threads())
+    return;
+  thrd_yield();
+}
+
+void __libcpp_thread_sleep_for(const chrono::nanoseconds& __ns) {
+  assert(__libcpp_is_threading_api_enabled());
+  __libcpp_timespec_t __ts = __thread_detail::__convert_to_timespec(__ns);
+  thrd_sleep(&__ts, nullptr);
+}
+
+// Thread local storage
+int __libcpp_tls_create(__libcpp_tls_key* __key, void (*__at_exit)(void*)) {
+  if (!__libcpp_is_threading_api_enabled())
+    return 0;
+  return tss_create(__key, __at_exit) == thrd_success ? 0 : EINVAL;
+}
+
+void* __libcpp_tls_get(__libcpp_tls_key __key) {
+  // ugly and devious way of getting cxa_exception_storage to work, but necessary if we want to
+  // keep all the runtime-dependent threading changes contained within internal_threading_support.h
+  if (!__libcpp_is_threading_api_enabled()) {
+    static struct {
+      void* caughtExceptions;
+      unsigned int uncaughtExceptions;
+    } eh_globals;
+    return &eh_globals;
+  }
+  // TODO: this won't work if __libcpp_is_threading_api_enabled() can change during program
+  // execution, because we may have skipped tss_create()
+  return tss_get(__key);
+}
+
+int __libcpp_tls_set(__libcpp_tls_key __key, void* __p) {
+  assert(__libcpp_is_threading_api_enabled());
+  return tss_set(__key, __p) == thrd_success ? 0 : EINVAL;
+}
+
+#  endif
+
+#endif // _LIBCPP_HAS_THREAD_LIBRARY_OPTIONAL && !_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL
+
+#endif // _LIBCPP_INTERNAL_THREADING_SUPPORT_H

libcxx/src/locale.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // On Solaris, we need to define something to make the C99 parts of localeconv
 // visible.
 #ifdef __sun__
 #define _LCONV_C99
 #endif
 
-#include "__threading_support"
+// This must come before anything file that #includes <__threading_support>
+#include "include/internal_threading_support.h"
 #include "algorithm"
 #include "clocale"
 #include "codecvt"
 #include "cstdio"
 #include "cstdlib"
 #include "cstring"
 #include "locale"
 #include "string"

libcxx/src/memory.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "memory"
 #ifndef _LIBCPP_HAS_NO_THREADS
-#   include "mutex"
+#   include "include/internal_threading_support.h"
 #   include "thread"
 #   if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
 #       pragma comment(lib, "pthread")
 #   endif
 #endif
 #include "include/atomic_support.h"
 
 _LIBCPP_BEGIN_NAMESPACE_STD

libcxx/src/random_shuffle.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "algorithm"
 #include "random"
 #ifndef _LIBCPP_HAS_NO_THREADS
-#   include "mutex"
+#   include "include/internal_threading_support.h"
 #   if defined(__ELF__) && defined(_LIBCPP_LINK_PTHREAD_LIB)
 #       pragma comment(lib, "pthread")
 #   endif
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_HAS_NO_THREADS

libcxxabi/src/cxa_exception_storage.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //
 //  This file implements the storage for the "Caught Exception Stack"
 //  https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html#cxx-exc-stack
 //
 //===----------------------------------------------------------------------===//
 
 #include "cxa_exception.h"
 
-#include <__threading_support>
+#include "include/internal_threading_support.h" // from libc++
 
 #if defined(_LIBCXXABI_HAS_NO_THREADS)
 
 namespace __cxxabiv1 {
 extern "C" {
     static __cxa_eh_globals eh_globals;
     __cxa_eh_globals *__cxa_get_globals() { return &eh_globals; }
     __cxa_eh_globals *__cxa_get_globals_fast() { return &eh_globals; }

libcxxabi/src/cxa_guard_impl.h

 #  endif
 #  if __has_include(<unistd.h>)
 #    include <unistd.h>
 #  endif
 #endif
 
 #include <limits.h>
 #include <stdlib.h>
-#include <__threading_support>
+#include "include/internal_threading_support.h" // from libc++
 #ifndef _LIBCXXABI_HAS_NO_THREADS
 #  if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
 #    pragma comment(lib, "pthread")
 #  endif
 #endif
 
 #if defined(__clang__)
 #  pragma clang diagnostic push

libcxxabi/src/fallback_malloc.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "fallback_malloc.h"
 
-#include <__threading_support>
+#include "include/internal_threading_support.h" // from libc++
 #ifndef _LIBCXXABI_HAS_NO_THREADS
 #if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
 #pragma comment(lib, "pthread")
 #endif
 #endif
 
 #include <stdlib.h> // for malloc, calloc, free
 #include <string.h> // for memset